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  Radar target detection method and radar apparatus using the sameUSPTO Application #: 20080100499Title: Radar target detection method and radar apparatus using the same Abstract: A radar target detection method in which an azimuth at which a target is located is detected on the basis of reception signals obtained through antenna elements of an array antenna by detecting a change in levels of spectrum peaks in an azimuth spectrum of reception signal intensities, calculating a level of correlation between the level change of each spectrum peak and a directivity pattern of the array antenna in an azimuth range corresponding to the spectrum peak, and determining an azimuth corresponding to one of the spectrum peaks having the highest corresponding correlation level to be the azimuth at which the target is located. (end of abstract) Agent: Dickstein Shapiro LLP - New York, NY, US Inventor: Tetsu Nishimura USPTO Applicaton #: 20080100499 - Class: 342 75 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20080100499. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001]1. Field of the Invention [0002]The present invention relates to radar target detection methods, and particularly to a target azimuth detection method and a radar apparatus using the detection method. [0003]2. Description of the Related Art [0004]Various radar apparatuses mounted in front portions of vehicles to detect targets have been developed. Such radar apparatuses transmit transmission waves towards predetermined detection areas including areas extending forward of the vehicles and receive reflection waves reflected from targets located within the detection areas. In a type of radar apparatus which has been in widespread use, at least either a transmitting antenna or a receiving antenna is configured as an array antenna composed of a plurality of antenna elements, and an azimuth of a target is detected on the basis of signals of a beam formed at different azimuths. [0005]Spacing between antenna elements constituting an array antenna may simultaneously constitute an advantage and a disadvantage of a radar apparatus. For example, when a distance between adjacent antenna elements is equal to or less than a half wavelength of a transmission signal, no grating lobes are generated. This allows precise detection of a target azimuth while decreasing the azimuth resolution. On the other hand, when the inter-element spacing is greater than a half wavelength of the transmission signal, an array antenna with a large aperture can be realized with a small number of antenna elements. This permits a radar apparatus to have a high azimuth resolution at low cost while resulting in generation of grating lobes. [0006]To overcome the above disadvantage, several techniques have been developed. [0007]For example, Japanese Unexamined Patent Application Publication No. 11-231040 discloses a radar in which an azimuth at which a directional intensity of a transmission/reception signal in a directivity pattern of an array antenna is null matches an azimuth at which grating lobes are generated. [0008]In addition, a radar disclosed in Japanese Unexamined Patent Application Publication No. 2000-258524 includes a first antenna capable of generating a beam in which intervals between grating lobes are small and a second antenna capable of generating a beam in which intervals between grating lobes are large. In this radar, the first antenna is used for detection of a target located at a distant position, and the second antenna is used for detection of a target located at a near position. [0009]Further, a radar device disclosed in Japanese Unexamined Patent Application Publication No. 2005-164370 utilizes the fact that azimuth angles at which grating lobes are generated depends on a transmission frequency. In this radar device, a transmission frequency is changed so that angles at which grating lobes are generated are changed with time. SUMMARY OF THE INVENTION [0010]However, angles at which grating lobes are generated depend on an azimuth of a target to be detected. Thus, in implementation of the radar disclosed in Japanese Unexamined Patent Application Publication No. 11-231040, a directivity pattern of the radar may have to be changed for each target to be detected. However, it is difficult to change the directivity pattern as necessary. Thus, this radar is not capable of uniformly suppressing grating lobes regardless of the azimuth of the target. [0011]In addition, the radar disclosed in Japanese Unexamined Patent Application Publication No. 2000-258524 realizes a plurality of antenna patterns by switching a relatively large number of antenna elements using a switch. Thus, in implementation of this radar, a large number of switches may be necessary, which results in high manufacturing cost. [0012]Further, in the radar disclosed in Japanese Unexamined Patent Application Publication No. 2005-164370, a transmission frequency is changed to switch an azimuth at which a grating lobe is generated. However, this radar is difficult to implement in terms of Radio Laws and manufacturing cost. [0013]The present invention has been made in view of the above circumstances. Accordingly, there is a need for a radar target detection method which allows precise detection of a target azimuth through simple processing even under conditions where grating lobes are generated. [0014]According to an embodiment of the present invention, there is provided a radar target detection method in which reception signal intensities at arbitrary specified azimuth angles within a predetermined detection area is calculated, on basis of reception signals obtained from transmitting and receiving of wave through antenna elements of an array antenna, and an azimuth at which a target is located is detected from the reception signal intensities arriving from the specified azimuth angles. This radar target detection method includes the following steps: (1) detecting change in levels of spectrum peaks in an azimuth spectrum of the reception signal intensities; (2) calculating a level of correlation between the level change of each spectrum peak and a directivity pattern of the array antenna in an azimuth range corresponding to the spectrum peak; and (3) determining an azimuth corresponding to one of the spectrum peaks of which the corresponding correlation level is high to be the azimuth at which the target is located. [0015]In this method, an azimuth spectrum of reception signal intensity based on a reception signal is time-sequentially formed, and change in the levels of a plurality of detected spectrum peaks is obtained. Then, a directivity pattern at an azimuth corresponding to each spectrum peak is read so that a level of correlation between the level change of the spectrum peak and a directivity pattern at the corresponding azimuth is detected. Note that the level change of a spectrum peak depends on the azimuth of a target and a directivity pattern. Thus, the level change of a spectrum peak corresponding to an azimuth of the target is similar to change in a directional level in the directivity pattern in a corresponding azimuth range. On the other hand, the level change of a spectrum peak corresponding to an azimuth at which the target is not present, i.e., at which grating lobes are generated, is not similar to change in the directional level in the directivity pattern in a corresponding azimuth range. Therefore, the azimuth at which the target is located can be obtained by detecting an azimuth corresponding to a peak level having a high correlation level with the directivity pattern. [0016]In the radar target detection, when an azimuth corresponding to one of the spectrum peaks changes with time, change in the level of a spectrum peak according to the azimuth change is detected, and the detected spectrum peak level change is approximated using a predetermined function so that a level of correlation between the spectrum peak level change and the directivity pattern is calculated. [0017]According to the method, in the detection of a level of correlation based on the level change of a peak level, the level change is approximated using a predetermined function and compared with a directivity pattern. With this arrangement, variation in the level change due to a factor other than the azimuth of a target and the directivity pattern can be suppressed. [0018]In addition, in the radar target detection method, linear approximation can be applied to a level change. [0019]Specifically, the level change is linearly approximated using a linear function and compared with the directivity pattern. This allows the comparison and the correlation level detection to be performed through simplified operations. [0020]In the radar target detection method, a spectrum peak level is corrected on the basis of a distance calculated from the reception signal. [0021]Specifically, the correction is based on the fact that the intensity of a reception signal depends on a distance of a target. With this arrangement, the relationship between an azimuth and the reception signal intensity is constant regardless of the target distance. [0022]In this method, a plurality of directivity patterns are set, and a level of correlation between change in a directional level due to switching of the directivity patterns and change in a spectrum peak level due to the switching is calculated for each azimuth corresponding to the individual spectrum peaks. Continue reading... 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